Charged particle radiation device

ABSTRACT

The present invention provides a scanning charged particle beam device including a sample chamber ( 8 ) and a detector. The detector has: a function of detecting light at least ranging from the vacuum ultraviolet region to the visible light region, of light ( 17 ) having image information which is obtained by a light emission phenomenon of gas scintillation when the sample chamber is controlled to a low vacuum (1 Pa to 3,000 Pa); and a function of detecting ion currents ( 11, 13 ) having image information which are obtained by cascade amplification of electrons and gas molecules. Accordingly, it becomes possible to realize a device which can deal with observation of various samples. Further, an optimal configuration of the detection unit is devised, to thereby make it possible to add value to an obtained image and provide users in wide-ranging fields with the observation image. In addition, the detector is made usable in combination with a detector for high vacuum, to thereby make it possible to provide wide-ranging users with the image, irrespective of the vacuum mode.

TECHNICAL FIELD

The present invention relates to a charged particle beam device whichuses a charged particle beam such as an electron beam and an ion beam,and more particularly, to a charged particle beam device which canrealize: means for detecting light in a region at least ranging from thevacuum ultraviolet light region to the visible light region; andcombination use of detection of light and ion current detection.

BACKGROUND ART

In a charged particle beam device typified by a scanning electronmicroscope, a sample is scanned with a finely focused charged particlebeam, whereby desired information (for example, a sample image) isobtained from the sample.

In such a charged particle beam device, up to now, observation utilizingreflection electrons with relatively high energy has been the mainstreamof an observation method for a low-vacuum (approximately 1 Pa to 3,000Pa) region. This is because, when a large number of gas moleculesexisting under low vacuum and electrons having an image signalrepeatedly collide against each other, the electrons having imageinformation lose energy thereof in this detection process and thuscannot reach a detector, so that the observation utilizing electronswith higher energy, that is, reflection electrons has been considered asa method which enables easier observation. The type of a material of anobservation sample, more specifically, an atomic number effect thereofremarkably appears on the obtained image, and hence this method isfrequently utilized at present for, particularly, surface observationand analysis of the surface in the materials field. Moreover, a highscanning speed (TV-Scan and the like) can be sufficiently dealt with,irrespective of a high vacuum or a low vacuum, and this is one of thereasons why this method has been utilized mainly for a detector.

Meanwhile, in recent years, a detection method of utilizing secondaryelectrons with small electron energy has been actively studied. Forexample, Patent Literatures 1, 2, and 3 exist. According to a large partof the existing methods, an electrode is placed in advance above asample, and cascade amplification is utilized in which secondaryelectrons generated from the sample are accelerated so as to repeatedlycollide for amplification against gas molecules existing inside of asample chamber.

Such a method is known as roughly two types of detection methods. One isan electron current detection method of detecting the amplifiedsecondary electrons themselves, and the other is an ion detection methodof detecting positive ions which are generated when the secondaryelectrons and the gas molecules collide against each other.

As representative examples of the conventional technologies, PatentLiterature 1 can be cited for the electron current method, and PatentLiteratures 2 and 3 can be cited for the ion current method.

Both of the images obtained according to the two methods closelyresemble a high-vacuum secondary electron image because a basic signalsource is the secondary electrons from the observation sample, and it ispossible to obtain an image having properties different from those of areflection electron image, that is, an image having information on anextreme surface of the observation sample.

CITATION LIST Patent Literature

-   Patent Literature 1: U.S. Pat. No. 4,785,182-   Patent Literature 2: JP Patent Publication (Kokai) No. 2001-126655 A-   Patent Literature 3: JP Patent Publication (Kokai) No. 2006-228586 A-   Patent Literature 4: JP Patent Publication (Kokai) No. 2003-515907 A-   Patent Literature 5: JP Patent Publication (Kokai) No. 2004-503062 A-   Patent Literature 6: U.S. Pat. No. 6,781,124 B2-   Patent Literature 7: U.S. Pat. No. 7,193,222 B2-   Patent Literature 8: U.S. Pat. No. 6,979,822 B1

Non Patent Literature

-   Non Patent Literature 1: Molecular Spectra and Molecular    Structure D. Van Nostrand Company, Inc.

SUMMARY OF INVENTION Technical Problem

On the other hand, unlike the high-vacuum secondary electron image andthe reflection electron image, there is a technical difficulty in termsof performance, that is, a difficulty in observation at a high scanningspeed. A conceivable reason therefor is that the ions having arelatively low flowing speed serve, in the cascade amplification processof the electrons and the ions, as an intermediary for the electronswhich form an image, and hence a difference occurs between an image tobe observed finally and the scanning speed of a primary electron beam.That is, there is a physical limitation of the detection speed.

Particularly in recent years, the need for an image obtained under lowvacuum is directed to acquisition of an extreme surface image of anobservation sample and secondary electron observation having qualitywhich is high enough to be comparable to the high-vacuum secondaryelectron image. In addition, fields which require such secondaryelectron observation under low vacuum widely range over abiological/chemical materials field, a geological field, a semiconductorfield, and the like.

Therefore, according to the present invention, detection means whichuses light as a signal source instead of electrons and ions, which havebeen conventionally used for detection, has been studied as the methodfor observing an extreme surface of a sample under low vacuum.

A detection method and an image observation method utilizing thisdetection means are disclosed as conventional technologies in PatentLiteratures 4 and 5 and Patent Literatures 6, 7, and 8 similar thereto.

When high energy is given to electrons, gas molecules, and ions whichare in a discharge state (including a plasma state), the electrons, thegas molecules, and the ions make the transition of an energy level fromthe ground state to the excited state, and return to the ground stateafter a short time (are kept in the excited state for several ns, andthen returns shortly). At the time of returning to the ground state, theelectrons, the gas molecules, and the ions emit photons corresponding tothe energy at the transition. This light is light having a spectrumspecific to, particularly, the type of gas, that is, an atom or amolecule. In the case of a detection method utilizing this lightemission phenomenon (gas scintillation), as a matter of course, thelight is detected. Accordingly, even a high scanning speed is dealt withat a sufficient response speed, and the obtained image closely resemblesthe high-vacuum secondary electron image.

Studying the above-mentioned literatures, there is not any descriptionof the type of light which is generated by the light emission phenomenonof the gas scintillation, and contents thereof do not fulfill furtherenhancement in performance and discovery of an added value.

In the case of utilizing this phenomenon, what is particularly importantis that a way of approaching optimization is different depending on whattype of light is handled.

The spectrum of light emission occurring under vacuum depends on thetype of introduced gas. The inventors of the present invention found outthat the wavelength of the light of this type is different from thewavelength of light emission (the vicinity of about 420 nm) of ascintillator normally used in an SEM, and spreads up to a vacuumultraviolet region with a further shorter wavelength.

Because the wavelength of the light spreads up to the vacuum ultravioletregion, it is considered that the technologies as disclosed in PatentLiteratures 4 and 5 have a limitation in effective detection. This isbecause, in the detector which uses the light normally used in the SEMas described above, a material of a light guide and a photomultipliertube are selected so as to suit the emission spectrum of thescintillator, and hence at least the transmittance of the light guideand the light-photoelectron conversion rate of the photomultiplier tubesignificantly decrease with regard to other wavelengths (see FIG. 4 andFIG. 5).

One object of the present invention is to provide an efficient detectionmethod of using light under low vacuum as a detection signal source.

Further, in addition to the above-mentioned object, combination use ofdetection of light and ion current detection has been studied.

For an approach thereto, in consideration of the properties of lightdescribed above, the structure itself of the conventional detectionmethod, particularly, the ion current detection is relatively simple,and hence means in which the method of detecting light having imageinformation and the ion current detection are combined with each otheris realizable enough.

As a result of an experiment, a difference in image quality could beconfirmed between: image quality obtained by the ion current detectionof the conventional detection method; and image quality obtained bydetecting the light having the image information. Both are images whichare considerably close to the high-vacuum secondary electron image, buta difference in contrast can be obtained therebetween depending on thetype of a sample to be observed. Accordingly, such a difference in imagequality is considerably useful, and it is suggested that observation ofvarious samples can be dealt with. This means that the above-mentionedmeans is useful to users in wide-ranging different fields in addition tousers in fields covered by the conventional technologies.

As a matter of course, in the case of handling the light having theimage information, a response speed sufficient to deal with high-speedscanning such as TV-Scan can be obtained.

In view of the above, a further object of the present invention is tobring out, to the maximum, performance and functions of each of thedetection method of using light as a detection signal source and thedetection method of using ions as a detection signal source and thusdevise an optimal configuration of a detection unit, to thereby addvalue to an obtained image and provide users in wide-ranging fields withthe observation image.

Solution to Problem

According to the experiment on which the present invention is based,although the wavelength of emitted light contained light in the visibleregion, the wavelength thereof contained, as expected, a large amount oflight ranging from the vacuum ultraviolet region to the visible region.Therefore, in the present invention, properties of light to be handledare sufficiently considered, so that a configuration capable ofdetection from the vacuum ultraviolet region to the visible region isadopted.

In view of the above, in the present invention, a detection unit whichdetects light includes a light guide (optical waveguide) made of amaterial which can transmit therethrough light at least ranging from thevacuum ultraviolet light region to the visible light region.

In addition, for the combination use of detection of light and iondetection, a sample chamber controlled to a low vacuum (1 Pa to 3,000Pa) is provided, and the detector includes: a control unit whichincludes a positive electrode in which +300 to +500 V is applied to atleast one electrode, detects light having image information by means ofa light guide (optical waveguide) disposed in a vicinity of the positiveelectrode, converts and amplifies the light into photoelectrons by meansof a photomultiplier tube coupled to the light guide, and then forms animage; and a control unit which detects, as a current signal, an ioncurrent having image information from another electrode having apotential different from that of the electrode, and forms an image.

Advantageous Effects of Invention

According to the present invention, it becomes possible to bring out, tothe maximum, performance and functions of each of the detection methodof using light under low vacuum as a detection signal source and thedetection method of using ions as a detection signal source, which is aconventional technology, and thus devise an optimal configuration of adetection unit, to thereby add value to an obtained image and provideusers in wide-ranging fields with the observation image.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic view of a scanning electron microscope which isone example of the present invention.

FIG. 2 is an enlarged view of a detector which is one example of thepresent invention and an Everhart Thornley detector (high-vacuumsecondary electron detector).

FIG. 3 are emission spectrum analysis result diagrams of the air (fromNon Patent Literature 1).

FIG. 4 are graphs showing light transmittances of acrylic and quartz(from data sheets of SUMIPEX, Sumitomo Chemical Co., Ltd./quartz,Shin-Etsu Chemical Co., Ltd.).

FIG. 5 are radiant sensitivity curve graphs of photomultiplier tubes(from a data sheet of Hamamatsu Photonics K.K.).

FIG. 6 is a schematic view illustrating a configuration example of anelectrode of the detector which is one example of the present invention.

FIG. 7 is a schematic view illustrating a configuration example of theelectrode of the detector which is one example of the present invention.

FIG. 8 is a schematic view illustrating a configuration example of alight guide and the electrode of the detector which is one example ofthe present invention.

FIG. 9 is a schematic view illustrating a configuration example of thelight guide and the electrode of the detector which is one example ofthe present invention.

FIG. 10 is a schematic view illustrating a configuration example of thelight guide and the electrode of the detector which is one example ofthe present invention.

FIG. 11 is a schematic view illustrating a configuration example of thelight guide and the electrode of the detector which is one example ofthe present invention.

FIG. 12 is a schematic view illustrating a configuration example of thelight guide and the electrode of the detector which is one example ofthe present invention.

FIG. 13 is a schematic view illustrating a configuration example of thelight guide and the electrode of the detector which is one example ofthe present invention.

FIG. 14 is a schematic view illustrating a configuration example of thelight guide and the electrode of the detector which is one example ofthe present invention.

FIG. 15 is a schematic view in which the light guide and a semi-in-typeobjective lens of the detector which is one example of the presentinvention are configured.

FIG. 16 is a view illustrating: an image acquired by the detector whichis one example of the present invention; and an SEM image acquiredaccording to a conventional method.

FIG. 17 is a view illustrating: an image acquired by the detector whichis one example of the present invention; and an SEM image acquiredaccording to a conventional method.

DESCRIPTION OF EMBODIMENTS

Hereinafter, some representative embodiments of the present inventionare described with reference to the drawings.

Embodiment 1

In the present embodiment, with regard to a scanning electron microscopewhich detects light having image information, an embodiment relating toa detector is described, the detector including: a detection unit whichdetects light having image information which is obtained by a lightemission phenomenon of gas scintillation which occurs in an observationsample chamber controlled to a low vacuum (for example, 1 Pa to 3,000Pa); and a detection unit which detects an ion current having imageinformation which is obtained by cascade amplification (gasamplification) of electrons and gas molecules.

FIG. 1 is a configuration view schematically illustrating an externalconfiguration of a scanning electron microscope in which a detectorwhich is one example of the present invention is disposed.

The scanning electron microscope illustrated in FIG. 1 includes: anelectron optical system including an objective lens 4; an observationsample chamber 8; a photomultiplier tube 21 which converts and amplifieslight detected by a light guide 20 into photoelectrons; a control unit22 which processes an outputted image signal to thereby form an image;similarly, a control unit 22 which processes a positive ion currentsignal derived from detected secondary electrons to thereby form animage; an image processing terminal 23 connected to the control units;and the like. The image processing terminal 23 includes: display meansfor displaying a formed image; information input means for inputtinginformation necessary for an operation of a device into a GUI displayedon the display means; and the like. It should be noted that respectiveconstituent elements of the electron optical system, for example, anacceleration voltage of a primary electron beam, a current and a voltageto be applied to each electrode, and the like are adjusted by anobservation condition control unit 24 in an automatic manner or inaccordance with a desired value which is inputted by a user on the imageprocessing terminal 23.

An electron source 1 included in the scanning electron microscope emitsa primary electron beam 2 of, generally, 0.3 kV to 30 kV. A multi-stagelens 3 is controlled into conditions suitable for observation, and has afunction of converging the primary electron beam. The objective lens 4similarly has a function of converging the primary electron beam so thatthe primary electron beam forms an image on a sample 5 to be observedand is focused on a point suitable for the observation. A deflector 25moves for scanning an irradiation position of the primary electron beamon the sample 5 within a desired range of an observation field of view.In addition, a scanning speed can be changed by a deflection signalcontrol unit 26 which controls the deflector 25. Along with theirradiation with the primary electron beam, secondary electrons 6 andreflection electrons 7 are emitted from the sample.

The degree of vacuum inside of the observation sample chamber 8 iscontrolled by opening/closing of a needle valve 28 for an atmosphereintroduction port 27 to the observation sample chamber 8. Thislow-vacuum SEM is provided with not only an observation mode under lowvacuum but also an observation mode under high vacuum, and at the timeof observation under high vacuum, the needle valve 28 is closed, wherebythe inside of the observation sample chamber 8 is kept in a high-vacuumstate of 10⁻³ Pa or smaller. At this time, the secondary electrons 6generated from the sample 5 are detected by a secondary electrondetector for high vacuum. Normally, the secondary electron detector forhigh vacuum detects the secondary electrons 6 by means of a detectorwhich is referred to as an Everhart Thornley detector 29 and includes ascintillator 55 and a photomultiplier tube. +10 kV 43 is applied to thevicinity of the scintillator, and further, in order to increase anefficiency of collecting the secondary electrons 6, a potential gradientis supplied to the inside of the observation sample chamber 8 by asecondary electron collector electrode 30 to which, typically, +300 V isapplied.

The reflection electrons 7 are detected by a reflection electrondetector 31 disposed immediately below the objective lens 4. Asemiconductor detector or a micro-channel plate is used for thereflection electron detector 31. In the case of using the semiconductordetector, the reflection electron detection can be performed even in theobservation mode under low vacuum to be descried later. Hereinafter, itis assumed that the reflection electron detector 31 is the semiconductordetector.

Signals derived from the detected secondary electrons and reflectionelectrons are electrically amplified, then are subjected to A/Dconversion by the control unit 22, and are displayed on the imageprocessing terminal 23 in synchronization with the scanning with theprimary electron beam 2. As a result, an SEM image within the range ofthe observation field of view can be obtained.

At the time of the observation under low vacuum, the inside of thesample chamber 8 is kept at a given gas pressure 19 by opening/closingof the needle valve 28. In addition, the potential of the secondaryelectron collector electrode 30 is switched to the ground potential. Thetypical gas pressure 19 inside of the sample chamber is 1 to 300 Pa, butcan be controlled up to 3,000 Pa in a special case.

Description is given below of a process of forming an image through thelight emission phenomenon of the gas scintillation and the cascadeamplification (gas amplification) of the electrons and the gasmolecules, for the purpose of the observation under low vacuum.

(1) In the sample chamber 8 controlled to a low-vacuum atmosphere (1 Pato 3,000 Pa), the secondary electrons 6 are generated from a sample 5which is irradiated with the primary electron beam 2.

-   -   (1)-1 Electrons and positive ions are generated by collision        between primary electrons and neutral gas molecules inside of        the sample chamber.    -   (1)-2 The secondary electrons 6 are generated from the sample 5.

(2) The secondary electrons 6 generated from the sample 5 are attractedby a first electrode 9 (+300 V to +500 V) disposed above the sample, andrepeatedly collide against the neutral gas molecules, so that theelectrons and the positive ions are generated by the cascadeamplification caused by an electron avalanche. Meanwhile, the reflectionelectrons have energy equal to that of the primary electrons, andcollide against the neutral gas molecules similarly, so that theelectrons and the positive ions are generated.

-   -   (2)-1 Electrons 10 derived from the secondary electrons and        positive ions 11 derived from the secondary electrons are        amplified by the electron avalanche of the secondary electrons        from the sample.    -   (2)-2 Similarly, electrons 12 and positive ions 13 derived from        the reflection electrons are generated.

A method of detecting the positive ion current in this stage, that is,the positive ions 11 derived from the secondary electrons and thepositive ions 13 derived from the reflection electrons, to therebyacquire an image is referred to as an ion current detection method.Further, with regard to the light emission phenomenon of the gasscintillation, an image is acquired through the following process.

(3) Energy is given to the electrons and the neutral gas molecules fromlarge energy in a plasma state (discharge) due to an electric fieldformed by the positive electrode above the sample, so that thetransition is made from a ground state 14 to an excited state 15.

-   -   (3)-1 The ground state 14 (stable atom/molecule state) to the        excited state 15 (unstable atom/molecule state).

(4) At the time of return from the unstable excited state to the groundstate, light having light energy corresponding to transition energy atthe transition to the excited state, that is, light (ultravioletlight/visible light) 17 having image information is generated.

-   -   (4)-1 Light having an emission wavelength peak which differs        depending on the type of the neutral gas molecules 18 and the        gas pressure 19 inside of the observation sample chamber 8 is        generated.

(5) The light emitted in the above item (4) is detected directly by asurface of the light guide 20, the light is converted and amplified intoelectrons by the photomultiplier tube (PMT) 21, and then the image isobserved via the formation control unit 22.

Here, FIG. 2 is an enlarged view of a detector 41 according to thepresent invention.

A positive voltage of +300 V to +500 V is applied to the first electrode9 disposed in the vicinity of the light guide 20, and a potentialgradient is supplied to the inside of the observation sample chamber.The gas scintillation in the above items (3) and (4) is generated bythis potential gradient at the same time as the cascade amplificationcaused by the electron avalanche in the above item (2). The positive ioncurrent having the image information in the above item (2), that is, thepositive ions 11 derived from the secondary electrons and the positiveions 13 derived from the reflection electrons, is detected by anothersecond electrode 32 having a potential different from that of the firstelectrode 9, passes through an electrical amplification circuit, and isformed as the observation image by the control unit 22.

On the other hand, the light 17 having the image information in theabove items (3) and (4) is detected directly by the light guide 20, istransmitted through the inside of the light guide, and enters thephotomultiplier tube 21 coupled to the light guide. After that, thelight is converted and amplified into photoelectrons, then is amplifiedwith a desired gain by an electrical amplification circuit 42, and isformed as the observation image by the control unit 22 similarly.

The light guide illustrated in FIG. 2 is configured to be capable ofsufficiently transmitting therethrough light ranging from the vacuumultraviolet region to the visible region. In addition, thephotomultiplier tube has performance which enables light ranging fromthe vacuum ultraviolet region to the visible region to be converted andamplified into photoelectrons.

With the use of FIG. 3, description is given below of the necessity todeal with the light ranging from the vacuum ultraviolet region to thevisible region, in order to detect the light of this type. FIG. 3 showemission spectrum analysis results 44 of the air according to Non PatentLiterature 1. As shown in the figures, main constituent moleculescontained in the air are nitrogen, and results derived from nitrogenmolecules are observed from the vacuum ultraviolet region to the visibleregion on the obtained emission spectrum. As described above, normally,the low-vacuum SEM is provided with a mechanism which keeps the insideof the observation sample chamber 8 at the given gas pressure 19 byopening/closing of the needle valve 28, and generally, the atmosphere(air) is introduced into the observation sample chamber 8. Accordingly,the spectrum of the light having the image information can be regardedas being substantially equivalent to the spectrum of nitrogen.

Here, in order to detect such light ranging from the vacuum ultravioletregion to the visible region, it is necessary that a light guide(optical waveguide) can sufficiently transmit therethrough the light inthis range and the light can be converted and amplified intophotoelectrons by the photomultiplier tube. With the use of thefollowing expressions, description is given of effects when the lightranging from the vacuum ultraviolet region to the visible region isdetected.

FIG. 4 show a light transmittance 45 of acrylic and a lighttransmittance 46 of quartz as material examples of the light guide. Asshown in the figures, quartz sufficiently transmits therethrough thelight ranging from the vacuum ultraviolet region to the visible region,compared with acrylic.

In addition, FIG. 5 show comparison between radiant sensitivity curvesof the photomultiplier tubes, that is, a radiant sensitivity curve 47 ofthe photomultiplier tube normally used in the SEM and a radiantsensitivity curve 48 of the photomultiplier tube used in the presentinvention.

Assuming that the number of photons of light which enters the lightguide is N, λ is the wavelength, h is a Planck's constant (6.626×10⁻³⁴Js), c is the speed of light in a vacuum (2.998×10⁸ m/s), anamplification factor of the photomultiplier tube is G, an influence ofthe light transmittance of the light guide is L(λ), a radiantsensitivity concerning a wavelength range dealt with by thephotomultiplier tube is P(λ), and a maximum wavelength and a minimumwavelength of the light which enters the light guide are respectivelyλ_(max) and λ_(min), a detection signal amount I which is taken out asan image signal from the photomultiplier tube is expressed as follows.

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 1} \right\rbrack & \; \\{I = {{GNhc}{\int_{\lambda_{\min}}^{\lambda_{\max}}{\frac{{L(\lambda)}{P(\lambda)}}{\lambda}\ {\lambda}}}}} & {{Expression}\mspace{14mu} (1)}\end{matrix}$

Then, according to Expression (1), conditions for increasing thedetection signal amount are as follows:

a. the amplification factor G of the photomultiplier tube is large;

b. the number N of photons of the light which enters the light guide islarge; and

c. the following right-hand side concerning the transmittance of thelight guide and the radiant sensitivity of the photomultiplier tube islarge.

$\begin{matrix}{\int_{\lambda_{\min}}^{\lambda_{\max}}{\frac{{L(\lambda)}{P(\lambda)}}{\lambda}\ {\lambda}}} & \left\lbrack {{Expression}\mspace{14mu} 2} \right\rbrack\end{matrix}$

Among these conditions, a. and c. depend on the material of the lightguide and the type of the photomultiplier tube. In general, theamplification factor of photoelectrons of the photomultiplier tube is10⁵ to 10⁶, and hence c. is considered to be the condition relating tothe entering light wavelength. Here, it is assumed that the wavelengthof the light which enters the light guide is from the maximum wavelengthλ_(max)=600 nm in the visible light region to the minimum wavelengthλ_(min)=200 nm in the vacuum ultraviolet region. In addition, thefollowing value is compared between: the case of applying specificationsnormally used in a standard SEM to the light guide and thephotomultiplier tube; and the case of applying thereto specificationsaccording to CLAIMS of the present invention.

$\begin{matrix}{\int_{\lambda_{\min}}^{\lambda_{\max}}{\frac{{L(\lambda)}{P(\lambda)}}{\lambda}\ {\lambda}}} & \left\lbrack {{Expression}\mspace{14mu} 3} \right\rbrack\end{matrix}$

-   -   Case of the configuration normally used in the SEM (from the        vicinity of 400 nm to 600 nm)

$\begin{matrix}{{\int_{\lambda_{\min}}^{\lambda_{\max}}{\frac{{L(\lambda)}{P(\lambda)}}{\lambda}\ {\lambda}}} = {\frac{211.6 \times 18.097}{160000} = 0.02393}} & \left\lbrack {{Expression}\mspace{14mu} 4} \right\rbrack\end{matrix}$

-   -   Case of the configuration which sufficiently deals with up to        the ultraviolet region (from 200 nm to 600 nm)

$\begin{matrix}{{\int_{\lambda_{\min}}^{\lambda_{\max}}{\frac{{L(\lambda)}{P(\lambda)}}{\lambda}\ {\lambda}}} = {\frac{368 \times 22.681}{160000} = 0.05217}} & \left\lbrack {{Expression}\mspace{14mu} 5} \right\rbrack\end{matrix}$

As shown above, an effect of about 2.18 times can be expected.

Hereinabove, the spectrum of the light in the light emission phenomenonof the gas scintillation is examined, and the detection signal amounttaken out as the image signal is examined, whereby importance of theabove-mentioned invention can be confirmed.

With these results, the use of a low-vacuum scanning electron microscopehaving an optimal configuration makes it possible to bring outperformance of the detection method using the light having the imageinformation.

It should be noted that it is desirable that a shape of the light guide20 have as large a detection area as possible, and further,irregularities may be formed on the surface of the light guide in orderto increase the surface area.

On the other hand, the structure for the detection of the ion currenthaving the image information can be relatively easily arranged. Becausethe electron avalanche (cascade gas amplification phenomenon) occursmost actively in the vicinity of the first electrode 9 to which apositive voltage is applied, the another second electrode 32 having apotential different from that of the first electrode 9 is provided atthe position as illustrated in FIG. 2, and the ion current, that is, thepositive ions 11 derived from the secondary electrons and the positiveions 13 derived from the reflection electrons are detected by theanother second electrode 32.

The image signal current thus obtained is subjected to signal processingby the control unit 22 as illustrated in FIG. 1 or as described above,so that observation thereof becomes possible.

It is considerably effective to dispose the electrodes in the vicinityof the light guide in this way, in terms of the fact that light(particularly, vacuum ultraviolet light) which is generated at a placein which the cascade amplification phenomenon is occurring can also bedetected efficiently. In the above-mentioned embodiment, the electrodesare disposed around the light guide, but similar effects can be expectedas long as the electrodes are disposed near the light guide.

Embodiment 2

The shapes of the first electrode 9 and the second electrode 32 aredescribed.

A main function of the first electrode 9 is to form a potential gradientinside of the observation sample chamber 8 adjusted to a desired gaspressure, specifically, to form a concentrated potential gradient whichactively causes the light emission phenomenon of the gas scintillationand the electron avalanche (cascade gas amplification phenomenon).

Accordingly, when the shape of the first electrode 9 is a mesh-likepattern with an interval of several μm to several mm, a plate-likepattern, a multi-bar-like pattern, or a ring-like pattern as illustratedin FIG. 6, effects of the phenomena can be obtained at low cost.Particularly, in the case where the electrode is formed into themulti-bar-like pattern, a leading end part thereof facing the sample 5may be formed into a sharp shape like a needle.

What is important for the shape of the first electrode 9 is that,because the light guide 20 which detects light is disposed in thevicinity thereof, it is necessary to form the first electrode 9 so asnot to block the light which enters the light guide 20. In addition, asdescribed above, the first electrode 9 controls the phenomena whichdirectly contribute to the image.

Therefore, control of the voltage of the first electrode 9 and the gaspressure of the observation sample chamber is made possible. An optimalcondition table according to each voltage, each gas pressure, and eachtype of gas may be experimentally obtained in advance, and a system inwhich an optimal condition is automatically selected only by inputting,on a GUI, necessary information requested by a user may be constructed.

In addition, a main function of the second electrode 32 is to detect theions 11 and 13 having the image information which are amplified by theelectron avalanche (cascade gas amplification phenomenon). Accordingly,the second electrode 32 is connected to the electrical amplificationcircuit 42 which performs amplification with a desired gain, and thedetected signal current needs to be electrically amplified immediately.In addition, because the extreme vicinity of the first electrode 9 towhich a positive voltage is applied is the optimal position, it isnecessary to form the second electrode 32 so as not to block the lightwhich enters the light guide 20, as pointed out with regard to the shapeof the first electrode 9.

Accordingly, similarly when the shape of the second electrode 32 is amesh-like pattern with an interval of several μm to several mm, aplate-like pattern, a multi-bar-like pattern, a ring-like pattern asillustrated in FIG. 6, or the like, effects can be obtained atrelatively low cost. With regard to the arrangement thereof, the secondelectrode 32 may be arranged on an inner side or an outer side of thefirst electrode 9.

Embodiment 3

FIG. 8 illustrates another embodiment of a charged particle beam deviceincluding a configuration of Claim 1. The present embodiment is the sameas Embodiment 1 except for the shape of the light guide. The shape ofthis light guide is differentiated from the others by taking theentering light and the shape of the light guide into consideration.

This light guide is tapered so as to be sharp toward the entering light,and is adapted to receive light which enters in various directions, on asurface thereof as far as possible. In order to transmit the lightwithout any loss, this light guide may be formed at an angle obtained byconsidering a total internal reflection critical angle ψ which iscalculated from a refractive index n₁ of the light guide and an enteringangle θ of the light as described below.

$\begin{matrix}{{\sin \; \psi} = {\frac{\sin \; \theta}{n} = {\frac{\sin \left( {90{^\circ}} \right)}{1.49} = {{0.6711\because\psi} = {{\sin^{- 1}(0.6711)} = {42.155{^\circ}}}}}}} & \left\lbrack {{Expression}\mspace{14mu} 6} \right\rbrack\end{matrix}$

In the case where the entering angle θ is 90 degrees, that is, the lightperpendicularly enters the surface of the light guide, because therefractive index n of a general material (acrylic PMMA resin) of thelight guide is around 1.49 to 1.5, the total internal reflectioncritical angle ψ is about 42 degrees according to the above expression.

In addition, in the case where the light guide has a columnar shape,only light which is emitted at within about 42 degrees corresponding toa half angle of the solid angle at the position, of the light receivedby a bottom surface of the columnar shape, is totally reflected on anouter circumferential surface inside of the light guide, and istransmitted to a surface thereof at another end. Such total internalreflection is transmission with small loss and high efficiency. Assumingthat a refractive index n₀ of the air=1, light which is isotropicallygenerated travels inside of the light guide while being confined thereinat the following ratio.

$\begin{matrix}{{\frac{1}{2}\left( {1 - {\sin \; \psi}} \right)} = {{\frac{1}{2}\left( {1 - \frac{n_{0}}{n_{1}}} \right)} = {16.7\%}}} & \left\lbrack {{Expression}\mspace{14mu} 7} \right\rbrack\end{matrix}$

As is apparent from the above expression, for one of examination pointsfor increasing a ratio of the transmission of light, it is preferable toselect a material having as large a refractive index as possible, andthis holds true for a high-vacuum secondary electron detector.

Embodiment 4

FIG. 9 illustrates another embodiment of the charged particle beamdevice including the configuration of Claim 1. The present embodiment isthe same as Embodiment 1 except for the shape of the light guide. Theshape of this light guide is differentiated from the others by takingthe entering light and the shape of the light guide into consideration.

This light guide is formed by bundling several thin linear opticalfibers 56 with a band 51. A detection light receiving surface of a lightguide 50 of the bundled optical fibers spreads in a trumpet-like shape,and detects light approaching the detector in various directions.Because the entering light enters the light guide substantially radiallyfrom the sample 5 which is the image signal source, in consideration ofthis, a method of detecting the light by means of leading end parts ofthe optical fibers which face various directions in the trumpet-likeshape is adopted.

The light is totally reflected inside of each of the bundled opticalfibers in the light guide 50 to be transmitted to a terminal end. Afterthat, the transmitted light is immediately guided to the photomultipliertube coupled thereto, and an image is formed via the electricalamplification circuit 42.

Embodiment 5

FIG. 10 illustrates another embodiment. The present embodiment is thesame as Embodiment 1 except for the shape of the light guide. The shapeof this light guide is specially directed to the method of detecting thelight having the image information, and is differentiated from theothers in that: a second light guide 39 is extended to the vicinity ofthe objective lens and is disposed immediately above the sample 5 to beobserved; and a fifth electrode 40 corresponding to the first electrode9 is configured together with the second light guide 39.

The present embodiment has an object to reduce a distance between thesample 5 and the light guide which is the detection unit, and hasfeatures that an observation working distance (WD) can be minimized,light can be detected with higher efficiency, and high-resolutionobservation is possible.

As illustrated in FIG. 10, the primary electron beam passes through thevicinity of the light guide according to the present embodiment, andhence electrical conductivity is given to the vicinity thereof. Lightgenerated by the light emission phenomenon of the gas scintillationwhich occurs between the sample 5 and the fifth electrode 40 isimmediately detected by the second light guide 39. The second lightguide 39 to be disposed may have a shape which surrounds the vicinity ofthe objective lens in a ring-like pattern as illustrated in FIG. 10.

Embodiment 6

FIG. 11 illustrates another embodiment of the present invention. Thepresent embodiment is the same as Embodiment 1 except for the lightguide 20, the first electrode 9, and the second electrode 32. Thepresent embodiment is differentiated from the others by applying asecondary electron detector for high vacuum to Embodiment 1 with thelight guide 20, the first electrode 9, and the second electrode 32 beingdifferent from those of Embodiment 1 as described above, and theembodiment for realizing this is illustrated in FIG. 11.

The light guide 20 is configured as a double-function light guide 33 andhas a structure which is divided into two functions for a high-vacuumsecondary electron detector and for detection of light under low vacuum.The double-function light guide 33 may be formed of one material and onepart, or may be formed of an optical fiber which can transmittherethrough light ranging from the vacuum ultraviolet region to thevisible region and can be bent into an arbitrary shape.

In addition, a third electrode 34 corresponding to the first electrode 9is disposed at a position at which the third electrode 34 does notobstruct the orbits of high-vacuum secondary electrons, for example, asillustrated in FIG. 11. Similarly to Embodiment 1, when the shapethereof is a mesh-like pattern with an interval of several μm to severalmm, a ring-like pattern, a plate-like pattern, a multi-bar-like pattern,or the like, effects can be obtained at relatively low cost.

In addition, similarly to Embodiment 1, a fourth electrode 38corresponding to the second electrode 32 is arranged on an inner side oran outer side of the third electrode 34. Similarly when the shapethereof is a mesh-like pattern with an interval of several μm to severalmm, a ring-like pattern, a plate-like pattern, a multi-bar-like pattern,or the like, effects can be obtained at relatively low cost.

An effect obtained by Embodiment 3 is that the charged particle beamdevice including the detector which is integrated irrespective of avacuum mode for the purpose of observing an image can be provided to auser.

In an existing scanning electron microscope, normally, a detectordedicated to high-vacuum secondary electron observation is applied underhigh vacuum, and detection dedicated to low-vacuum secondary electronobservation using ion current detection is applied under low vacuum.Accordingly, the observation sample chamber 8 is equipped with ports forrespectively disposing the two.

On the other hand, in the case of the configuration according to thepresent embodiment, a port for the detector to be prepared in theobservation sample chamber can be configured only by a port for thedetector integrated irrespective of the vacuum mode. Against the needsof recent years that an increasing number of users desire a wide varietyof observations, this effect can provide a scanning electron microscopehaving scalability for attaching special auxiliary equipment which isspecially designed in accordance with a customer's desire, in additionto various analysis devices (other devices which deal with X-rays, suchas WDX: wavelength-dispersive X-ray analyzer and EDX: energy-dispersiveX-ray analyzer, EBSP: crystal particle analyzer, CL: cathodeluminescence spectrometer, Raman spectrometer, and the like). Inaddition, owing to a difference in obtained image quality, it ispossible to be free from the concept of the vacuum mode and observe acharacteristic secondary electron image, and it is thus possible toexpect an effect that a wide range of users can seamlessly performsurface observation without paying attention to the type of a sample tobe observed.

Embodiment 7

FIG. 12 illustrates another embodiment. The present embodiment issimilar to the configuration described in Embodiment 1, but isdifferentiated from the others in that the used photomultiplier tube isan existing photomultiplier tube, that is, a wavelength range dealt withthereby is the visible region (particularly, the vicinity of 420 nm).

Because the wavelength range dealt with by the photomultiplier tubewhich converts and amplifies light into photoelectrons is the visibleregion, in order to efficiently convert the light into thephotoelectrons, it is necessary to convert the wavelength of detectedlight containing light in the vacuum ultraviolet region into light inthe visible region by some sort of means. Such means therefor can berealized by applying a phosphor which reacts to light in the vacuumultraviolet region to emit light in the visible region, to the surfaceof the light guide 20, for example, as illustrated in FIG. 12. Thephosphor of this type contains such components as BaMgAl₁₀O₁₇:Eu and thelike, and is used for a PDP (plasma display) of recent years and thelike. In the case of using the phosphor which emits light in reaction tolight in the vacuum ultraviolet region, a slight delay in response(several hundred μs) is anticipated compared with direct detection bythe light guide, but a high scanning speed in the SEM is normally up to0.033 s/frame (up to 33 ms/frame), and hence this delay in response doesnot become problematic. Irregularities are formed on a surface of alight guide 35 for wavelength conversion used in the present embodiment,whereby the application of the phosphor to the surface may befacilitated. In addition, such irregularities may be formed in advanceinto a shape obtained by considering a critical reflection angledepending on the material of the light guide as in Embodiment 2.

Embodiment 8

Next, on the basis of an idea similar to that of Embodiment 7, it isconsidered that the wavelength of entering light is converted. As amatter of convenience, description is given by using the detector 41 ofthe present invention in FIG. 2.

The light guide 20 used in FIG. 2 is replaced with the light guide 35for wavelength conversion, and at this time, a photomultiplier tubenormally used in the SEM is used without any change.

The light guide for wavelength conversion, which converts light in theultraviolet region into light in the visible region, has some problem inconversion efficiency, but is advantageous in that the photomultipliertube normally used in the SEM can be used. In this case, although themethod considerably resembles that of Embodiment 7, sufficient effectscan be expected only by simply changing the material of the light guidewhile omitting the trouble of applying the phosphor.

Embodiment 9

FIG. 13 illustrates another embodiment. The present embodiment issimilar to the configuration described in Embodiment 1, but isdifferentiated from the others in that a transparent electrode 36 whichcan sufficiently transmit therethrough the light having the imageinformation is vapor-deposited on the surface of the light guide, as anelectrode corresponding to the first electrode 9 in the vicinity of thelight guide.

In recent years, it is becoming possible to easily utilize technologiesdeveloped for a PDP (plasma display). The transparent electrodeaccording to the present embodiment is one of those technologies, andthis is applied to the present invention. The type of light to be dealtwith, that is, light in the vacuum ultraviolet region, light emission ofthe phosphor, and the technology for the PDP including the transparentelectrode can be sufficiently applied to a detector structure accordingto the present embodiment. As illustrated in FIG. 13, a thin film havingelectrical conductivity and high transparency, such as an ITOvapor-deposited film, is vapor-deposited on a surface of a combinedlight guide 37 having high transparency and transmission. This thin filmhaving electrical conductivity and high transparency is immediatelycaused to function correspondingly to the first electrode 9, whereby itis possible to generate the light emission phenomenon of the gasscintillation and the cascade gas amplification phenomenon as describedin Embodiment 1 and Embodiment 3. What is greatly different fromEmbodiment 1 and Embodiment 3 is that there is no fear that suchstructures as the first electrode 9 and the second electrode 32 aredisposed in the vicinity of the light guide which is the detection unit,to thereby block the entering light.

It is desirable that irregularities be formed on the surface of thecombined light guide 37, and protrusions thereof may be formed so thateffects similar to those of the first electrode 9 described inEmbodiment 1 can be obtained.

In the present embodiment, only the transparent electrode may be simplyvapor-deposited on the surface of the light guide, and alternatively, asillustrated in FIG. 13, it is also possible to adopt a double structureusing the combined light guide 37 having one side on which thetransparent electrode 36 is vapor-deposited and another side to whichthe phosphor described in Embodiment 5 is applied.

Embodiment 10

FIG. 14 illustrates another embodiment. The present embodiment isdifferentiated from the other embodiments in that: an optical path isbranched by using the light guide 20 and a branching light guide (madeof an optical fiber) 65; the optical path of the light guide is used atthe time of a high vacuum, whereas the optical path made of the opticalfiber is used at the time of a low vacuum; and detection and imageformation are performed by using one photomultiplier tube.

In the case of a light guide made of acrylic, quartz, or the like whichcan transmit therethrough light having a wide wavelength, it isdifficult to branch an optical path thereof in terms of problems of amaterial, production, and the like. In addition, a direction of lightemitted inside of the sample chamber is not necessarily one, and henceit is desirable that the optical path can be freely bent and can befreely disposed at an optimal position.

The configuration illustrated in FIG. 14 can solve the above-mentionedproblems and troubles at a time. On this occasion, as described in(Embodiment 1), it is desirable to provide a photomultiplier tube havinga feature of being operable from the ultraviolet region to the visibleregion. The electrode as described in the above-mentioned embodiments isprovided around an optical fiber leading end detection unit used forlight detection under low vacuum (in FIG. 14, around a leading end partof the branching light guide 65 and the first electrode 9).

Embodiment 11

In relation to the configuration illustrated in FIG. 8, in the opticalpath (light guide), it is possible to enable detection not only by asurface facing the sample but also by a side surface of the light guide.According to a general usage of the light guide, detection is performedby a planar surface facing the sample, but can be performed also by aside surface of the light guide in order to detect emitted light to themaximum.

Embodiment 12

FIG. 15 illustrates another embodiment. The present embodiment isdifferentiated from the other embodiments in that: high resolution isachieved by using a semi-in-type objective lens 62; observation in botha high-vacuum mode and a low-vacuum mode is made possible by providingan exhaust orifice 66 for vacuum operation; a gas amplification actionin which secondary electrons 64 and gas molecules collide against eachother is utilized, the secondary electrons 64 being moved up inside ofthe objective lens by an influence of a leakage magnetic field generatedby the semi-in-type objective lens, the gas molecules remaining insideof the objective lens; and light which is emitted at the time of the gasamplification action is detected for forming the image.

In the case where the semi-in-type objective lens is used under lowvacuum, in general, the exhaust orifice for vacuum operation is providedat a position of a main surface of the lens corresponding to a maximummagnetic field. About 100 μm to 1,000 μm is selected as a hole diameterof the orifice, and the secondary electrons generated from the sampleare moved up by the influence of the magnetic field of the semi-in-typeobjective lens, pass through this hole, and are drawn into the lens. Ina charged particle beam device which utilizes the action of moving upthe secondary electrons by the magnetic field, only the secondaryelectrons which are moved up from the surface of the sample can becaptured by E×B (Wien filter) at a detection efficiency substantiallyequal to 100% without affecting the primary electron beam.

The present embodiment provides a detection method under low vacuumwhich is greatly different from those of the other embodiments in thatthe above-mentioned action is utilized to thereby realizehighly-efficient detection of light and high resolution by means of alarger amount of secondary electrons and lower aberration of thesemi-in-type objective lens.

Lastly, effects of obtained images are illustrated in FIG. 16 and FIG.17.

The light and the ion current each having the image information aredetected at the same time, and are observed at the same time, so that anobservation picture as illustrated in FIG. 16 can be photographed. FIG.16 illustrates an ion current image 57 having the image information andan image 58 obtained by detecting the light having the imageinformation. As illustrated in FIG. 16, both the images considerablyclosely resemble a high-vacuum secondary electron image, but contraststhereof which are partially different can be observed. There is a highchance that a large number of users in a biological/chemical materialsfield, a geological field, a semiconductor field, and the like desire toobserve, at the same time, images having contrasts which are differentdepending on the type of the sample 5.

In addition, FIG. 17 illustrates an image 59 at the time of high-speedscanning by detecting the ion current having the image information andan image 60 at the time of high-speed scanning by detecting the lighthaving the image information. The comparison between these images showsparticularly characteristic performance when the light having the imageinformation is detected. Originally, the detection is performed by usinglight, and hence, as described above, this makes a difference inresponse performance of an image signal from the ions having arelatively low flowing speed. In addition, the amplification isperformed not by the electrical amplification circuit as in the ioncurrent detection method but by the photomultiplier tube. Therefore, itis possible to respond at high speed to a signal for forming anobservation image by the control unit 22 in accordance with a highscanning speed of a TV (up to 0.033 s/frame).

REFERENCE SIGNS LIST

-   -   1 electron source    -   2 primary electron beam    -   3 multi-stage lens    -   4 objective lens    -   5 sample    -   6 secondary electrons    -   7 reflection electrons    -   8 observation sample chamber    -   9 first electrode    -   10 electrons derived from secondary electrons    -   11 positive ions derived from secondary electrons    -   12 electrons derived from reflection electrons    -   13 positive ions derived from reflection electrons    -   14 ground state    -   15 excited state    -   16 transition energy    -   17 light having image information (ultraviolet region/visible        region)    -   18 gas molecules    -   19 gas pressure    -   20 light guide    -   21 photomultiplier tube (PMT)    -   22 (image formation) control unit    -   23 image processing terminal    -   24 observation condition control unit    -   25 deflector    -   26 deflection signal control unit    -   27 atmosphere introduction port    -   28 needle valve    -   29 Everhart Thornley detector (high-vacuum secondary electron        detector)    -   30 secondary electron collector electrode    -   31 reflection electron detector    -   32 second electrode    -   33 double-function light guide    -   34 third electrode    -   35 light guide for wavelength conversion    -   36 transparent electrode    -   37 combined light guide    -   38 fourth electrode    -   39 second light guide    -   40 fifth electrode    -   41 detector of the present invention    -   41 electrical amplification circuit    -   43 +10 kV    -   44 emission spectrum analysis results of air    -   45 light transmittance of light guide (acrylic)    -   46 light transmittance of quartz    -   47 radiant sensitivity curve of photomultiplier tube normally        used in SEM    -   48 radiant sensitivity curve of photomultiplier tube used in the        present invention    -   49 tapered light guide    -   50 light guide of bundled optical fibers    -   51 band    -   52 phosphor which reacts to light in ultraviolet region to emit        light    -   53 light having image information in visible region    -   54 overall SEM control unit    -   55 scintillator for high-vacuum secondary electron detector    -   56 optical fiber thin line    -   57 ion current image    -   58 image of light having image information    -   59 image at the time of high-speed scanning by detecting ion        current    -   60 image at the time of high-speed scanning by detecting light        having image information    -   61 earth electrode    -   62 semi-in-type objective lens    -   63 E×B (Wien filter)    -   64 secondary electrons moved up by magnetic field    -   65 branching light guide (made of optical fiber)    -   66 exhaust orifice for vacuum operation

1. A charged particle beam device, comprising: a charged particlesource; a charged particle optical system which includes a lens, andfocuses a primary charged particle beam emitted from the chargedparticle source to scan a sample therewith; a detector which detects asignal particle which is generated from the sample by the scanning withthe primary charged particle beam; and a control unit which controls thelens, the charged particle beam device acquiring a sample image by usinga signal of the detection means, wherein: the charged particle beamdevice further comprises a sample chamber controlled to a low vacuum (1Pa to 3,000 Pa); and the detector includes: a control unit whichincludes a positive electrode in which +300 to +500 V is applied to atleast one electrode, detects light having image information by means ofa light guide (optical waveguide) disposed in a vicinity of the positiveelectrode, converts and amplifies the light into photoelectrons by meansof a photomultiplier tube coupled to the light guide, and then forms animage to thereby enable observation; and a control unit which detects,as a current signal, an ion current having image information fromanother electrode having a potential different from that of theelectrode, and forms an image. 2-14. (canceled)